1. Field of the Invention
The invention relates to an object-support column of the type including an end unit, a guide tube having an end which is connected to the end unit, and a pneumatic tube surrounding the guide tube and the end unit, the pneumatic tube having a conical section with a diameter reduction surrounding the end unit.
2. Description of the Related Art
Object-support columns of this type are used, for example, in vertically adjustable chairs or tables. For attaching the object-support column, for example, to a chair support, a pneumatic tube is configured with a diameter reduction at one end. This diameter reduction may be, for example, of conical form. For multiple usage, the cone is standardized in its dimensions.
This makes it possible for the object-support column to be exchanged irrespective of a particular manufacturer. Arranged within the pneumatic tube is a guide tube in which, in turn, a displacer, usually a piston rod with a piston, is guided in an axially moveable manner. Installed as an end unit at the end which is directed toward the diameter reduction is a valve housing in which a switchable valve which influences a flow connection as a fluid connection between the guide tube and an annular space running between the pneumatic tube and the guide tube is arranged. The valve housing has a guide stub which is pushed into the guide tube. By way of its outer contour, the valve housing is supported on the inner wall of the pneumatic tube and thus centers the guide tube in relation to the pneumatic tube.
The displacement length of the object-support column is dependent on the useable length of the guide tube minus the length of the piston. If it is necessary to maintain a predetermined spacing between the diameter reduction and the other end of the pneumatic tube, then there is no point in shortening the valve housing between the end of the guide tube and the inner wall of the pneumatic tube in order to assign the saved length to the guide tube. If the guide tube were to be lengthened, it would butt against the pneumatic tube in the inner region of the diameter reduction and the above-described annular space would no longer exist.
Alternatively, it would be possible to shorten the guide stub, but the increases in length which can be achieved are rather modest. In addition, or alternatively, it would be possible to reduce the wall thicknesses of the guide tube and of the pneumatic tube and, with a given external diameter of the pneumatic tube and with an identical internal diameter of the guide tube, to achieve a wider annular space. It would thus be possible, in turn, to lengthen the guide tube until a minimum spacing has been reached between the end-side outer edge of the guide tube and the nearest region of the inner wall of the pneumatic tube. In the case of a product which has already been in use for a long time, the wall thicknesses are largely used up. Even smaller wall thicknesses would require high-strength materials which, in turn, have an adverse effect on the cost.